Robust amphibious aircraft

ABSTRACT

A robust amphibious air vehicle incorporates a fuselage with buoyant stabilizers and wings extending from the fuselage. At least one lift fan is mounted in the fuselage. Movable propulsion units carried by the wings are rotatable through a range of angles adapted for vertical and horizontal flight operations.

BACKGROUND INFORMATION Field

Embodiments of the disclosure relate generally to amphibious aircraftand more particularly to an aircraft operable as an unmanned air vehicle(UAV) with horizontal takeoff/landing or vertical takeoff/landingcapability and enhanced water stability for a perched condition in highsea state conditions.

Background

The surface of the earth is over 71% water resulting in huge maritimeareas to service for transportation, military operational needs andsearch and rescue as well as interacting with objects on the sea surfaceincluding recovery. Historically and currently there have been veryeffective amphibious aircraft that were able to provide long rangeoverwater transportation and search as well as sea landing/takeoff forinteraction with objects on the sea surface. However, there have been novehicle systems that can address the full range and conditions thatoccur, specifically long range flight and long term loiter at sea withthe capability to accommodate high sea states and maintain operationalcapability without damage.

It is therefore desirable to provide an air vehicle system whichaccommodates these requirements.

SUMMARY

Exemplary embodiments provide a robust amphibious air vehicle having afuselage with buoyant stabilizers and wings extending from the fuselage.At least one lift fan is mounted in the fuselage. Movable propulsionunits carried by the wings are rotatable through a range of anglesadapted for vertical and horizontal flight operations.

The embodiment disclosed provide a method for operation of a robustamphibious air vehicle wherein the air vehicle is deployed from a homestation in Vertical Takeoff. The air vehicle transitions to horizontalflight and dashes to a remote location. Assets are deployed and the airvehicle lands on the water surface. The air vehicle then loiters on thewater in a perched condition. The air vehicle may then take off tomonitor assets in flight, recover or deploy assets from/to the seasurface with reduced time hover; and, return to home station.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, functions, and advantages that have been discussed can beachieved independently in various embodiments of the present disclosureor may be combined in yet other embodiments, further details of whichcan be seen with reference to the following description and drawings.

FIG. 1A is a downward pictorial representation of the air vehicle inhovering operation;

FIG. 1B is an upward pictorial representation of the air vehicle inhovering operation;

FIG. 1C is a front view of the air vehicle in hovering operation;

FIG. 1D is a top view of the air vehicle in hovering operation;

FIG. 1E is a side view of the air vehicle in hovering operation;

FIG. 2 is a downward pictorial representation of the air vehicleconfigured for horizontal flight;

FIG. 3 is a detailed view with the ducted fan partially sectioned;

FIG. 4A is a representation of the air vehicle with the wings in a firsttop folded configuration;

FIG. 4B is a representation of the air vehicle with the wings in asecond top folded configuration;

FIG. 5 is a representation of the air vehicle with the wings in a sidefolded configuration;

FIG. 6 is a representation of the air vehicle with the wings in a firsttransition stage to a side folded configuration;

FIGS. 7A and 7B are a top view and side view representation of analternative embodiment of the air vehicle with conformal engagement ofside folded wings;

FIG. 8 is a representation of the air vehicle partially submerged in apogo configuration;

FIG. 9 is a block diagram of a ballast control system;

FIG. 10 is a representation of the air vehicle employing motioncompensated recovery of surface articles;

FIG. 11 is a representation of an alternative embodiment of the airvehicle;

FIG. 12A is a representation of the alternate embodiment with the wingsin a first transition position;

FIG. 12B is a representation of the alternate embodiment with the wingsin a second transition position;

FIG. 12C is a representation of the alternate embodiment with the wingsin a horizontal flight position;

FIG. 12D is a representation of the alternate embodiment in a hardsurface landed configuration;

FIG. 13 is a block diagram of the ballast control system for thealternative embodiment.

FIG. 14 is a flow chart of a method for operational use of the disclosedair vehicle; and,

FIGS. 15A and 15B are a flow chart of a method for operational use of analternative embodiment of the air vehicle.

DETAILED DESCRIPTION

The embodiments described herein provide a robust amphibious air vehiclethat has vertical flight capability for shipboard operations (landingand takeoff), winged operations to offer extended ranges, folding orrobust configuration to perch on the sea like a lifeboat or stabilizedplatform and provide an air vehicle with capability for motioncompensated recovery of surface articles.

Referring to the drawings, FIGS. 1A through 1E disclose a firstembodiment of a robust amphibious air vehicle 10. The air vehicle 10incorporates a fuselage 12 having buoyant stabilizers, in the exemplaryembodiment pontoons 14 laterally displaced from a centerline 16 at thelateral extents of the fuselage. While two pontoons are shown in theexemplary embodiments multiple pontoons on each side of the fuselage maybe employed. To accommodate desired vertical take-off and landingcapability at least one lift fan is mounted in the fuselage 12. For theembodiment shown, two lift fans 18 a and 18 b, longitudinally spaced onthe centerline 16, are employed. Use of two lift fans allows pitchcontrol in vertical or hovering operations with variable relative thrustin the fans. Wings 20 a and 20 b extend from the fuselage 12 for liftcarrying capability in horizontal flight to provide extended range andspeed capability for the air vehicle. Movable propulsion units, wingtipmounted ducted fans 22 a and 22 b for the exemplary embodiment, provideadditional lift in a first vertical position as shown in FIGS. 1A and 1Band are rotatable through a range of angles, +A through −A, and from thevertical to a horizontal position as shown in FIG. 2 to provide thrustfor horizontal flight. Angle and thrust variation of the ducted fans 22a, 22 b allows yaw and roll control in vertical or hovering operations.Winged flight operation with the ducted fans 22 a, 22 b in thehorizontal position allows higher speeds and longer range operation thana pure rotorcraft with the capability for low speed, low energyconsumption loiter with aerodynamic lift. While shown as mounted to thewingtips in the exemplary embodiment, the movable propulsion units maybe supported within the wing planform in alternative embodiments.

Ducted fans 22 a and 22 b are employed in the exemplary embodiment notonly for aerodynamic efficiency but for shielding of the propulsionrotors 24 a and 24 b during water operation. However, in alternativeembodiments unducted tilt-rotors may be employed. Additionally, use ofteetering rotor systems or controllable rigid rotor systems in the wingmounted fans and/or lift fans with cyclic control may be employed foradditional control capability in vertical or hovering operations.

The ducted fans 22 a, 22 b for the exemplary embodiment incorporatesupplemental buoyancy elements 26. The supplemental buoyancy elements 26are mounted on a centerline 28 of the propulsion fans 24 a, 24 bdownstream of the fan discs as seen in FIG. 1B and shown in detail inFIG. 3. A buoyant chamber 30 is supported by a connecting strut 32 whichmay be an extension of the engine/motor nacelle 34 of the propulsionrotor 24 a, 24 b. In alternative embodiments the supplemental buoyancyelements may extend from or be incorporated in the aft periphery of theduct of the ducted fans 22 a, 22 b The supplemental buoyancy elements 26provide flotation to assist in maintaining the ducted fans 22 a, 22 bout of the water and, additionally, by their location at or near thewingtips provides an extended lateral moment arm 36 (best seen in FIG.1D) from the vehicle centerline 16 for enhanced roll stability of theair vehicle 10 in the water. While vertical takeoff and landing areanticipated as a normal water operational mode the shoulder mountedconfiguration of the wings in the exemplary embodiment allows clearanceof the ducted fans 22 a, 22 b in the horizontal operationalconfiguration to allow horizontal takeoff and landing of the air vehicle10 on the water.

The air vehicle 10 is specifically adapted to remain “perched”, floatingon the water, for extended periods of time to allow deployment at remotedispersed locations without the need for loitering in flight. The highlystable nature of the fuselage arrangement while on the water withbuoyant stabilizers such as pontoons 14 a, 14 b and additionalstabilization with the supplemental buoyancy elements 26 may be furtherenhanced for survivability in high sea states by providing wing foldingmechanisms. As represented in FIG. 4A, the wings may be folded onto thetop or deck 13 of the fuselage 12 using articulating mechanisms 36.Actuatable universal joints 38 (best seen in FIGS. 1C and 1D) may beemployed in mounting the ducted fans 22 a, 22 b to the wingtips suchthat, in addition to the articulation for hovering control andtransition to horizontal flight, rotation with respect to the wings 20a, 20 b is allowed such that the fans and the supplemental buoyancyelements 26 remain adjacent the pontoons 14 a, 14 b with the wings inthe folded condition. For the fuselage top wing fold, this secondaryplane of rotation for the fans is substantially parallel to the wingchord.

FIG. 4B shows an alternative top folding mechanism wherein the wings 20a, 20 b are bifurcated on a midspan chord for first folding elements 21a, folding inward onto the deck 13 of the fuselage 12, and secondfolding elements 21 b, folding outboard back onto the first foldingelements. This configuration avoids the requirement for rotation of theducted fans 22 a, 22 b, naturally placing the fans adjacent the sides ofthe fuselage.

In an alternative embodiment, the wings 20 a, 20 b may be rotated forfolding against sides 40 of the fuselage 12 as represented in FIG. 5.Articulating mechanisms 42 allow rotation of the wings 20 a, 20 bthrough a first 90-degree rotation as shown in FIG. 6 followed by asecond perpendicular 90-degree rotation to the position of FIG. 5. As inthe prior embodiment, actuatable universal joints 38 allow rotation ofthe ducted fans 22 a, 22 b such that the fans and the supplementalbuoyancy elements 26 remain adjacent the pontoons 14 a, 14 b with thewings in the folded condition. However, in this embodiment, theactuatable universal joints 38 rotate the ducted fans in a planesubstantially perpendicular to the wing chord.

As also seen in FIGS. 5 and 6, the pitch/yaw control surfaces 44 a, 44 bare deflectable to a downward orientation to act as directional ruddersor stabilizers when the air vehicle 10 is on the water. For theembodiment shown, two pitch/yaw control surfaces 44 a and 44 b areemployed in a “ruddervator” configuration. In alternative embodimentswith a vertical control surface and horizontal surfaces mounted on theempennage, the horizontal surfaces may be deflected downward for thewater rudder or stabilizer configuration.

In alternative embodiments, particularly with the ducted fans mountedwithin the wing planform, a reduced chord length in the wings and/orincreased depth of the fuselage allows conformal engagement of the wingsand fuselage as shown in FIGS. 7A and 7B.

Survivability of the air vehicle 10 when loitering on the water in highsea states may be further enhanced by at least partially submerging thevehicle. Structures which are partially submerged in an orientationsubstantially vertical to the ocean surface (a “pogo” orientation) havebeen shown to be highly stable and resistant to damage in high seas. Theair vehicle 10 may be equipped with fillable ballast tanks 46 in thepitch/yaw control surfaces 44 a, 44 b, ballast tanks 48 in the empennage(in the present embodiments the aft portions 50 a and 50 b of thepontoons 14 a, 14 b) and ballast tanks 52 in the supplemental buoyancyelements 26 as represented in FIG. 8. A ballast control system 54 asshown in FIG. 9 interconnected to the ballast tanks allows filling ofthe ballast tanks to reorient the air vehicle 10 to a vertical positionas seen in FIG. 8. The ballast control system employs a compressor 56and/or compressed air tanks 58 operably connected to the ballast tanksthrough valves 60. Water valves 62 controllable by a microprocessor 64are opened with the air vehicle on the water thereby filling the ballasttanks. Controlled sequencing of the valves may be employed, for example,filling of the ballast tanks 46 to create a tail low condition, followedby filling of ballast tanks 48 for submerging the empennage, withfilling of the ballast tanks 52. Natural buoyancy of the pontoons 14 a,14 b (which may be supplemented with sealed buoyancy tanks 66 shown inFIG. 7) balances the air vehicle 10 in the pogo position. The ductedfans 22 a, 22 b and the supplemental buoyancy elements 26 may be rotatedas shown to optimize the vertical alignment of the overall air vehiclein the pogo position. Returning to a normal horizontal floating positionas seen in FIG. 5 is accomplished by the microprocessor 64 activatingthe compressor and opening the air valves 60 to blow the ballast tanksfollowed by closing of the water valves 62 resulting in normal buoyancyof the aft portions 50 a, 50 b of the pontoons, the pitch/yaw controlsurfaces 44 a, 44 b and the supplemental buoyancy elements 26 followedby closing of the water valves 62.

While represented with the side folding wing configuration for theembodiment shown in FIG. 8, the top folding configuration of FIG. 4A or4B may be similarly employed in the pogo capable arrangement.

Integration of motion compensated recovery of surface articles asdisclosed in U.S. Pat. No. 8,591,161 (the disclosure of which isincorporated herein by reference) and shown notionally in FIG. 10, isemployed for operational enhancement of the air vehicle 10. Sonobuoys,or similar operational components, or fuel supply canisters may beautomatically retrieved using a hoist cable mounted maneuvering system(HCMMS) 70 from containers 72 on ships 74 or prepositioned floatingbarges.

In an exemplary operational scenario, the air vehicle 10 may employmotion compensated recovery/movement of arrayed Cohesive Sensor Buoys(i.e. intermittent coherent network processing) as a mission asset.Having the flight capability of the air vehicle 10 expandspassive/active sonar sensitivity/coverage up to several orders ofmagnitude while adding above water acoustic sensing with appropriateinstrumentation on the air vehicle 10 with a control system 76. Use ofcollaborative autonomy in the air vehicle 10 leverages mature OpenSystems Architecture software for local awareness and remote command andcontrol. Suspended array position and time synchronization challengesare addressed using multiple passive/active sound, light and networktechniques. Above water directional acoustic sensing by the air vehiclecaches data, preprocesses, monitors, locates and identifies sources.Adaptive software defined radio (SDR) robust networks share data betweensurface elements. Multi-Mode resilient Position, Navigation and Timingis addressed with robust Position Navigation Time-Targeting (PNT-T)using proven Micro-GCU related technologies. The air vehicle 10,employing Collaborative Autonomy, deploys, enables operations, recovers,transits and redeploys sensor buoy arrays for anti-submarine warfare(ASW), fleet protection, search/rescue and mission/logistics transportoperations.

In alternative embodiment, the air vehicle 10 is simplified to provide ahighly stable semisubmerged pogo arrangement for on surface loiteringwith a wing deployment design and unique operational scenario forsimplified design. Fuselage 12 is shaped with a bulbous forward section80 tapering to a substantially conical empennage 82. This embodimentwith a ballast system to be described in greater detail subsequently,allows the air vehicle to be partially submerged in a pogo orientationwith a very smooth exterior surface similar to current ocean buoydesigns. This provides a highly stable configuration for on surfaceloitering even in very high sea states. A propulsion system 84 ismounted to the empennage 82. For the exemplary embodiment, thepropulsion system employs two ducted fans 22 a, 22 b mounted with ahorizontal stabilizer 86. As in previously described embodiments, theducted fans 22 a, 22 b are mounted with rotating joints 38 and arerotatable through a range of angles, +B through −B, as shown in FIG. 11.Angle and thrust variation of the ducted fans 22 a, 22 b allows yaw androll control in vertical or hovering operations. Wings 20 a, 20 breceived in the contour of the fuselage in a folded position areextendible from the fuselage, as will be described in detailsubsequently, for horizontal flight operations.

The air vehicle 10 in the embodiment of FIG. 11 operates with transitionto a water landing/loiter directly from vertical flight. As the fuselageenters the water a ballast system compensates for any buoyancy of thefuselage to partially submerge the fuselage in a pogo orientation. Thepropulsion system 84 remains clear of the water and extraction of theair vehicle from the water is accomplished using direct vertical liftwith purging of any ballast as the fuselage is withdrawn from the waterafter extraction. Loitering in place or short range flight operationsmay be conducted with the propulsion system operating in a verticalflight mode. If extended distance or higher speeds are required, the airvehicle 10 ascends to a predetermined altitude and the wings areunfolded from the fuselage and a rapid descent is initiated to provideaerodynamic lift on the wings and the air vehicle is then recovered fromthe dive to horizontal flight using standard aerodynamic control and/orthrust vectoring by the propulsion system.

As shown in FIG. 12A, wings 20 a and 20 b are extended from the fuselageon axles 88. The wings 20 a, 20 b may then be rotated about a first axison the axles 88 to a secondary position as shown in FIG. 12B followed byrotation about a perpendicular axis using joints 90 to a horizontalflight position as seen in FIG. 12C. The transition steps described withrespect to FIGS. 12B and 12C may be reversed in certain operationalscenarios. Standard aerodynamic controls such as ailerons may beemployed on the wings 20 a, 20 b or rotation on axles 88 may providedifferential lift for roll control. Horizontal stabilizer 84 may berotatable or include an elevator for aerodynamic pitch control. Angularrotation of ducted fans 22 a, 22 b may provide thrust vectoring foradditional pitch, roll and/or yaw control in the horizontal flight mode

Return to vertical flight mode may be accomplished by slowing the airvehicle 10 to produce aerodynamic stall on the wings 20 a, 20 b with apendulum recovery by the propulsion system 84 using thrust and angularcontrol of the ducted fans 22 a, 22 b. The wings 20 a, 20 b may then befolded into the fuselage reversing the extension operation previouslydescribed with respect to FIGS. 12A-12C.

As seen in FIG. 12D, the air vehicle 10 may be operated in verticalflight mode for takeoff and landing on hard surfaces such as ship decksor for land operations. A dolly 92 having wheels 94 and a support frame96 may be positioned to receive and support the fuselage 12 in avertical position. Alternatively, wheeled or skid landing gear may beexternally or retractably mounted to the air vehicle. The air vehiclemay take off vertically from the dolly and land vertically on the dolly.Alternatively, the air vehicle may be landed in the water and retrievedvia crane.

FIG. 13 shows the simplified ballast control system for the alternativeembodiment. A ballast tank 98 (seen in phantom in FIG. 11) supported inthe forward section 80 is provided with at least one valve 100controllable to receive water for flooding the tank to increase ballastfor vertical (pogo) orientation in the water. A compressor 102 and/orpressure tanks 104 are provided and connected through a expulsion valve106 to expel ballast water from the ballast tank as the air vehicle iswithdrawn from the water. A microprocessor controller 108 is adaptedwith control modules for valves 100 and 106, and compressor 102,pressure tanks 104 and valve 106 for ballast intake and expulsion.

FIG. 14 shows a method for operation of an air vehicle as disclosedherein. The air vehicle 10 is deployed from a small ship or other homestation by vertical takeoff, step 1402. Motion compensated recovery ofassets to be deployed is accomplished, step 1404. The air vehicle thentransitions to horizontal flight, step 1406, and dashes to a remotelocation for loiter, step 1408, or to deploy the assets, step 1410.Steps 1404, 1406 and 1408 may be repeated as necessary for assetdeployment. If extended loiter is desired, the air vehicle 10 lands onthe water surface, step 1412, and loiters in a perched condition, step1414. Wings may be folded for perching, step 1416. For extended perchingor in high sea states, ballast tanks in the air vehicle may be flooded,step 1418, to orient the air vehicle in a pogo mode. On command or uponpreprogrammed mission guidelines, the air vehicle is removed from pogomode, step 1420, returns to flight configuration, step 1422, and takesoff, step 1424. The air vehicle may then monitor assets in flight,recover or deploy assets from/to the sea surface with reduced time hover(including floating fuel canisters), step 1426. Upon mission completion,the air vehicle returns to home station, step 1428.

FIGS. 15A and 15B show a method for operation of the alternativeconfiguration of the air vehicle as described herein. The air vehicle 10is deployed from a small ship or other home station by vertical takeoff,step 1502. Motion compensated recovery of assets to be deployed isaccomplished in vertical flight mode, step 1504. The air vehicle thentransitions to horizontal flight, as previously described, by unfoldingthe wings, step 1505, a diving conversion to aerodynamic flight andrecovery to a horizontal flight mode, step 1506. The air vehicle thendashes to a remote location, step 1508, for loiter or to deploy theassets, step 1510. If loiter and/or deploy steps are to be accomplishedin vertical flight mode, the air vehicle decelerates from horizontalflight through aerodynamic stall and executes a pendulum recovery tovertical flight with folding of the wings, step 1511 as previouslydescribed. Steps 1504, 1506, 1508, 1510 and 1511 may be repeated asnecessary for asset deployment. If extended loiter is desired, the airvehicle 10 lands on the water surface in vertical flight mode, step1512, the ballast tank if filled, step 1514 and air vehicle loiters in apogo condition, step 1516. On command or upon preprogrammed missionguidelines, the air vehicle is extracted vertically from the water usingthe propulsion system, step 1518, with offloading of ballast, step 1520,and returns to vertical flight mode, step 1522. Return to horizontalflight mode step 1524 may be accomplished as described in Step 1506 asrequired. The air vehicle may then return to station, step 1526, returnto vertical flight mode, step 1528 as described in step 1511, and land,step 1530.

Having now described various embodiments of the disclosure in detail asrequired by the patent statutes, those skilled in the art will recognizemodifications and substitutions to the specific embodiments disclosedherein. Such modifications are within the scope and intent of thepresent disclosure as defined in the following claims.

What is claimed is:
 1. An air vehicle comprising: a fuselage havingbuoyant stabilizers; wings extending from the fuselage, said wingsadaptable to fold adjacent the fuselage; at least one lift fan mountedin the fuselage; and, movable propulsion units carried by the wings,said movable propulsion units rotatable through a range of anglesadapted for vertical and horizontal flight operations, wherein themovable propulsion units are wing tip mounted ducted fans, said wing tipmounting including an articulating universal joint for rotation of theducted fan in a plane perpendicular to a wing chord for placement of theducted fan adjacent sides of the fuselage.
 2. The air vehicle as definedin claim 1 wherein the buoyant stabilizers are laterally displaced froma vehicle centerline to provide enhanced lateral stability.
 3. The airvehicle as defined in claim 2 wherein the buoyant stabilizers compriseat least two pontoons on opposed lateral extents of the fuselage, thefuselage having a deck extending between the pontoons.
 4. The airvehicle as defined in claim 1 wherein the at least one lift fancomprises two lift fans longitudinally spaced on a vehicle centerline.5. The air vehicle as defined in claim 1 further comprising supplementalbuoyancy elements extending aft of propulsion rotors in the ducted fans.6. The air vehicle as defined in claim 5 wherein the supplementalbuoyancy elements comprises a buoyant chamber supported by a connectingstrut extending from an engine/motor nacelle of a propulsion rotor inthe ducted fan.
 7. The air vehicle as defined in claim 1 furthercomprising: a plurality of ballast tanks adapted for filling to createrotational negative buoyancy placing the fuselage in a substantiallyvertical orientation with respect to a water surface; and, a ballastcontrol system for venting of the ballast tanks to return the fuselageto a substantially horizontal orientation.
 8. The air vehicle as definedin claim 1 wherein the at least one lift fan comprises two lift fanslongitudinally spaced on a vehicle centerline and further comprisingsupplemental buoyancy elements extending aft of propulsion rotors in theducted fans.
 9. The air vehicle as defined in claim 8 wherein thesupplemental buoyancy elements comprises a buoyant chamber supported bya connecting strut extending from an engine/motor nacelle of apropulsion rotor in the ducted fan.
 10. The air vehicle as defined inclaim 1 wherein the buoyant stabilizers comprise at least two pontoonson opposed lateral extents of the fuselage, the fuselage having a deckextending between the pontoons and further comprising a buoyant chambersupported by a connecting strut extending from an engine/motor nacelleof a propulsion rotor in each ducted fan.
 11. A method for operation ofan air vehicle comprising: deploying the air vehicle from a home stationin vertical takeoff, said vehicle having a fuselage having buoyantstabilizers; wings extending from the fuselage, said wings adaptable tofold adjacent the fuselage; at least one lift fan mounted in thefuselage; and, movable propulsion units carried by the wings, saidmovable propulsion units rotatable through a range of angles adapted forvertical and horizontal flight operations, wherein the movablepropulsion units are wing tip mounted ducted fans, said wing tipmounting including an articulating universal joint for rotation of theducted fan in a plane perpendicular to a wing chord for placement of theducted fan adjacent sides of the fuselage; transitioning the air vehicleto horizontal flight; dashing to a remote location; deploying assets;landing the air vehicle on the water surface; loitering in a perchedcondition; taking off to monitor assets in flight, recover or deployassets from/to the sea surface with reduced time hover, and, returningthe air vehicle to home station.
 12. The method as defined in claim 11further comprising recovering assets to be deployed with a hoist cablemounted maneuvering system (HCMMS).
 13. The method as defined in claim11 further comprising folding the wings for perching.
 14. The method asdefined in claim 13 wherein the step of folding the wings comprisesarticulating the wing adjacent sides of a fuselage of the air vehicleand rotating articulating propulsion units with supplemental buoyancyelements in a plane perpendicular to a wing chord for placement adjacentsides of a fuselage of the air vehicle.
 15. The method as defined inclaim 11 wherein the air vehicle further comprises a plurality ofballast tanks adapted for filling to create rotational negative buoyancyplacing the fuselage in a substantially vertical orientation withrespect to a water surface; and, a ballast control system for venting ofthe ballast tanks to return the fuselage to a substantially horizontalorientation; and the step of loitering in the perched condition furthercomprises: flooding ballast tanks in the air vehicle to orient the airvehicle in a pogo mode; and, on command or upon preprogrammed missionguidelines vent the ballast tanks to remove the air vehicle from pogomode to return to flight configuration.
 16. A method for enhancedperformance of an air vehicle comprising: deploying an air vehicle froma home station by vertical takeoff, said vehicle having a fuselagehaving buoyant stabilizers; wings extending from the fuselage, saidwings adaptable to fold adjacent the fuselage; at least one lift fanmounted in the fuselage; and, movable propulsion units carried by thewings, said movable propulsion units rotatable through a range of anglesadapted for vertical and horizontal flight operations, wherein themovable propulsion units are wing tip mounted ducted fans, said wing tipmounting including an articulating universal joint for rotation of theducted fan in a plane perpendicular to a wing chord for placement of theducted fan adjacent sides of the fuselage; transitioning the vehicle tohorizontal flight; dashing to a remote location; vertically landing theair vehicle on the water surface; loitering in a perched condition;taking off from the water surface vertically; and returning the airvehicle to the home station.